The role of C1GALT1C1 in lipopolysaccharide-induced IgA1 aberrant O-glycosylation in IgA nephropathy.

IgA1 aberrant O-glycosylation is one of the main pathogenetic features of IgA nephropathy (IgAN). This study attempted to determine the role of C1GALT1C1 in aberrant IgA1 O-glycosylation induced by lipopolysaccharide (LPS) and identify potential therapeutic targets in IgAN. Lymphocytes isolated from 22 patients with IgAN and 17 normal controls were cultured for 3 to 7 days with or without LPS and 5-azacytidine (5-AZA). Expression levels of C1GALT1C1 mRNA and protein were measured by real-time PCR and Western blot analysis, respectively. Concentration of IgA1 and level of O-glycosylation were determined by ELISA and Vicia villosa (VV) lectin-binding assay. Correlation analysis was performed between the expression of C1GALT1C1 protein and IgA1 O-glycosylation. Lymphocytes from patients with IgAN secreted more IgA1 than that from normal controls after LPS stimulation (P=0.26, 0.002 and 0.005 on the 3rd, 5th and 7th day, respectively) which could be inhibited by 5-AZA (P=0.001, 0.025 and 0.001 on the 3rd, 5th and 7th day, respectively). Moreover, LPS stimulation could obviously inhibit C1GALT1C1 expression in patients with IgAN (decreased by 71%, 82% and 92% on the 3rd, 5th and 7th day, respectively; P < 0.001), and cause a significant decrease of IgA1 O-glycosylation compared with normal controls (P=0.004, 0.003 and 0.03 on the 3rd, 5th and 7th day, respectively). When 5-AZA was added, the level of C1GALT1C1 expression increased dramatically (1.98, 5.53 and 8.97 times on the 3rd, 5th and 7th day, respectively; P < 0.001) along with an increase of IgA1 O-glycosylation (P=0.295, 0.09 and 0.003 on the 3rd, 5th and 7th day, respectively). However, normal controls showed no significant change in C1GALT1C1 expression and IgA1 O-glycosylation after LPS stimulation (P > 0.05). LPS induced IgA1 aberrant O-glycosylation and suppressed C1GALT1C1 expression in patients with IgAN. Upregulation of C1GALT1C1 expression by 5-AZA could reverse the IgA1 aberrant O-glycosylation. These results suggest that C1GALT1C1 may play a key role in the regulation of IgA1 O-glycosylation.